This invention is concerned with static vent units and particularly but not exclusively with static vent units for use on rotary wing aircraft such as helicopters.
Static vent units are used on both fixed and rotary wing aircraft to sense the ambient pressure of the air through which the aircraft is flying. This provides an indication of the altitude at which the aircraft is flying and, in combination with a pressure signal sensed by a forward facing pitot tube, an indication of the airspeed and, for fixed wing aircraft, the Mach number.
For this reason, static vent units have ideally to be located in a position where the local ambient pressure varies only with altitude and not with other features such as airspeed and relative wind direction, and are therefore usually located in the sides of an aircraft fuselage.
However, it is extremely difficult to find a suitable location where the local pressure remains unaffected by disturbing factors throughout the entire operating range so that the local ambient pressure is often in error by a significant amount, resulting in inaccurate information to the pilot.